Federal officials are again warning Americans new terrorist attacks may be imminent, and Iowa Senator Chuck Grassley says this is -not- a case of the government crying wolf.Based on what he calls “credible” information, U-S Attorney General John Ashcroft says the renewed attacks may come this week, but it’s not known where, how or when. Grassley says it’s the duty of our elected leaders to try to keep the nation stable and safe. He says that’s exactly what happened with the announcement yesterday.It’s the second time this month such a warning has been issued.As more anthrax cases are diagnosed, rumors are circulating whether small pox will be the next biological weapon unleashed on the U-S. Senator Grassley says federal officials are making huge orders of drugs to combat that potential threat.The U-S Health and Human Services department has asked Congress to provide more than half-a-billion dollars to speed development and purchase of the vaccines. Up to 300-million doses of the small pox vaccine have been ordered, enough to cover the entire U-S population. Long after the disease had been eliminated in the U-S, Grassley says a few people came into the nation decades ago from Mexico who were infected.Most Americans born before 1972 were vaccinated against small pox, but health officials say the immunity has likely worn off. Very few people born after 1972 have been vaccinated and would quickly succumb to the disease. Small pox kills 30-percent of infected victims and easily spreads from person to person, both by touch and through coughing, sneezing or even speaking.